1. Technical Field
The present invention generally relates to a liquid crystal device, and more particularly, to a liquid crystal device that operates in an OCB (Optically Compensated Birefringence or Bend) mode. In addition, the invention further relates to an electronic apparatus that is provided with such an optically compensated birefringence liquid crystal device.
2. Related Art
In a typical configuration of an optically compensated birefringence liquid crystal device of the related art, a liquid crystal layer that is sealed between a pair of substrates, which are provided opposite to each other, can switch its alignment/orientation state between so-called splay alignment and so-called bend alignment. In their initial orientation state, liquid crystal molecules of a liquid crystal layer are in splay alignment. An alignment-state transition voltage is applied thereto in order to switch their orientation state from the initial splay alignment to the bend alignment, the latter of which is the orientation mode used for image display. At the time of image display operation thereof, an OCB-mode liquid crystal device of the related art changes its transmission factor dependent on the degree of curves in the bend alignment so as to perform optical modulation. Since the OCB-mode liquid crystal device performs optical modulation for image display in such a way, it offers an advantage of fast/quick response.
In the following description, the fundamental configuration and operation of an optically compensated birefringence liquid crystal device of the related art is explained. FIG. 18 is a set of diagrams that schematically illustrates an example of the pixel configuration of an OCB-mode liquid crystal device of the related art; or, more specifically, FIG. 18A shows a plan view thereof whereas FIG. 18B shows a sectional view taken along the line XVIIIB-XVIIIB of FIG. 18A. As illustrated in FIG. 18B, each pixel 44 of an OCB-mode liquid crystal device of the related art has a sandwiched structure that is made up of an element substrate 10, a counter substrate 30, and a liquid crystal layer 40 that is sealed between the element substrate 10 and the counter substrate 30. As illustrated in FIG. 18A, a plurality of gate lines 12 is formed on the base substrate substance of the element substrate 10. As further illustrated therein, a plurality of source lines 14 is formed on the base substrate substance of the element substrate 10. The gate lines 12 extend in parallel with one another. The source lines 14 also extend in parallel with one another. A TFT (Thin Film Transistor) element 20 is formed at a position corresponding to each intersection of the gate line 12 and the source line 14. A pixel electrode 16 is connected to each of the TFT elements 20. Each of the pixel electrodes 16 is formed at an area that is surrounded by two gate lines 12 arrayed adjacent to each other and two source lines 14 arrayed adjacent to each other. In a plan view, a clearance is formed between the pixel electrode 16 and the gate line 12. In like manner, a gap is formed between the pixel electrode 16 and the source line 14 as viewed in two dimensions.
In order to cause transition in the orientation state of the liquid crystal layer 40 from the initial splay alignment to the bend alignment, as a first step thereof, a transition voltage is applied between the gate line 12 and the pixel electrode 16. As a result of the application of the transition voltage between the gate line 12 and the pixel electrode 16, an electric field F is generated in the liquid crystal layer 40. As illustrated in FIG. 18B, the electric field F has an electric line of force that connects the gate line 12 and the pixel electrode 16. The orientation/alignment direction of liquid crystal molecules 40a contained in the liquid crystal layer 40 changes in accordance with the directional component of the generated electric field F. As a result thereof, a transition force for switching the orientation state of the liquid crystal molecules 40a thereof from the splay alignment to the bend alignment works thereon. At the initial stage of the transition, transition nuclei for switching the orientation state of the liquid crystal molecules 40a thereof from the splay alignment to the bend alignment are generated at each concave region (i.e., concave area) 60 or in the neighborhood thereof. As illustrated in FIG. 18A, the concave region 60 is formed between the gate line 12 and the pixel electrode 16. Thereafter, another transition voltage is applied between the pixel electrode 16 and a common electrode 36. The common electrode 36 is formed on the counter substrate 30. As a result of the application of the transition voltage between the pixel electrode 16 and the common electrode 36, a bend alignment area spreads over the pixel electrode 16, which starts from the transition nucleus. In this way, the orientation state of the liquid crystal molecules 40a of the liquid crystal layer 40 transitions from the splay alignment to the bend alignment in an OCB-mode liquid crystal device of the related art. An example of the orientation-state transition method/scheme of the related art explained above is disclosed in JP-A-2001-296519.
In the typical orientation-state transition method/scheme used in an OCB-mode liquid crystal device of the related art explained above, a transition nucleus is mainly generated at a position corresponding to, for example, in or over, the concave area 60, which is outside the pixel electrode 16. In order to spread a bend alignment area over the pixel electrode 16 from the initial starting point described above, it is necessary for it to “climb over” the pixel electrode 16, that is, overcome a level difference between the concave area 60 and the pixel electrode 16. For this reason, the orientation-state transition method/scheme used in the OCB-mode liquid crystal device of the related art explained above has a disadvantage in that it inevitably requires a greater force for successfully spreading the bend alignment area. For this reason, if the alignment-state transition method/scheme used in the OCB-mode liquid crystal device of the related art explained above is adopted, it is necessary to apply a relatively high transition voltage thereto in order to successfully spread the bend alignment area over the pixel electrode 16. Since a relatively high transition voltage is required, the orientation-state transition method/scheme used in the OCB-mode liquid crystal device of the related art explained above has a disadvantage in that it consumes greater power at the time of splay-to-bend alignment transition operation. Generally speaking, it is necessary to continue the application of a transition voltage thereto until a bend alignment area that is generated at a transition nucleus as a starting point spreads to the entire region over the pixel electrode 16. In connection therewith, time required for the completion of the spreading of a bend alignment area to the entire region over the pixel electrode 16 becomes longer as a pixel becomes larger. In the technical field to which the present invention pertains, a liquid crystal device in which the transition can be completed in a shorter time period with a lower transition voltage so as to achieve reduced power consumption is awaited.